Self-retracting lifelines – also referred to as retractable fall arresters, fall arrest lifelines, fall protection yoyos, fall arrest blocks and self-retracting lanyards- have been expertly designed to detect when a worker is about to fall and tightens the cable to a halt. They work like a seatbelt, when you pull on the line lightly it pays out and retracts smoothly, but when you abruptly yank the line, the system stops and thus arrests the fall to stops the wearer from encountering a potentially life-threatening injury.